I appreciate your concern. If the environment is that wet then the drill stays inside more out of concern for the longevity of the drill then my own! There don't seem to be any obvious ground sources in the vicinity of the winches on the cabin top and the GFCI outlet that the drill is plugged into is yet another safety net that I have in place. Here is my disclaimer: Use at your own risk and don't try this at home. I'm a trained professional.

We use a Milwaukee Winch Buddy system which we put together via Ebay. It has become an indispensable tool, not just for raising the sail, but hoisting people up the mast for necessary repair. And as on any boat, when hoisting someone up the mast is usually when the battery craps out! Usually get about 6-8+ hoists out of a charge. We charge the battery on the inverter while doing long range cruising. We use bungee cords and store it tucked against the settee bulkhead by the nav station, so it is accessible and out of the way.